1. Field of the Invention
The invention relates to tools for inserting implants into bone and more particularly to drivers for suture anchors.
2. Description of the Related Art
A common injury, especially among athletes, is the complete or partial detachment of tendons, ligaments or other soft tissues from bone. Tissue detachment may occur during a fall, by overexertion, or for a variety of other reasons. Surgical intervention is often needed, particularly when tissue is completely detached from its associated bone. Currently available devices for tissue attachment include screws, staples, suture anchors and tacks.
Arthroscopic tissue attachment is commonly practiced in shoulder rotator cuff and instability procedures. Typically, an anchor loaded with suture is fixated to bone using an inserter-type device. The suture is normally slidably attached to the anchor through an eyelet or around a post, such that a single length of suture has two free limbs. The suture limbs typically are carried along the exterior of the inserter, usually within a groove or other exterior channel, or within the interior of the inserter. After the anchor is inserted into the bone, one limb of the suture is passed through soft tissue to be repaired such as a tendon or labrum. The two ends of the suture are then tied to each other, thereby capturing the soft tissue in a loop with the anchor. Upon tightening the loop, the soft tissue is approximated to the bone via the anchor.
Some anchor inserters are utilized to push an anchor into a pre-drilled hole in a bone, such as shown in U.S. Pat. No. 7,381,213 by Lizardi, while other inserters apply torque to a helically threaded anchor to rotate the anchor into a pre-formed hole, such as illustrated in U.S. Patent Publication No. 2008/0147063 by Cauldwell et al. Certain anchors are asymmetrical and require relatively small force for insertion, while other, symmetrical anchors must be driven at a higher forces to ensure sufficient fixation between the anchor and the bone. Some anchors benefit from internal support by a substantially rigid tip of an inserter while being driven into bone.
The tip of an implant driver typically is constructed of a hardened material which may be strong but brittle. In other words, the driver tip usually lacks ductility. Large strains imparted on a material may result in failure of the implant and/or the driver tip. Failure of the driver tip may result in breakage which must be retrieved from the patient. Strains may arise when an implant is being inserted at an off-axis angle into a hole in bone, or when the implant is partially or fully inserted and a laterally-directed load is applied to the driver handle.
One type of asymmetric, push-in anchor is disclosed by Pedlick et al. in U.S. Pat. No. 6,961,538. In one embodiment, an installation tool has a substantially rigid elongated rod with a somewhat flexible distal end that encourages a plow-like edge of a wedge-shaped anchor to dig into the wall of a pre-formed hole in bone. The installation tool does not appear to be capable of providing any internal support to the anchor during insertion.
Another type of asymmetric anchor is described by Lizardi in U.S. Pat. No. 6,527,795. A tapered anchor has a flared portion on its trailing end. An insertion tool may include a flexible portion that allows the tool to bend when pressure is exerted to generate a compressive force that is greater on one side of the anchor, which toggles or rotates the anchor.
A further consideration is having sufficient yet releasable attachment between the anchor and the inserter. Some systems rely on an interference fit, while others utilize a threaded engagement. A implant inserter device is described by Stoffel et al. in U.S. Patent Publication No. 2010/0292704 having an inner sleeve which collapses from an undeformed position to a deformed position to grip an implant.
It is therefore desirable to have an improved inserter which can apply sufficient insertion force to an implant without damaging the implant and without breakage.